Extracting chemical concepts with effective fragment orbitals

ENG- The first part of the work focuses on ligands that bind to metal centers and chemical substituents. It presents new ways to measure how ligands donate or accept electrons (their donor-acceptor properties) by directly analyzing their wavefunctions, offering a more consistent and quantitative alternative to traditional models. Additionally, it redefines how substituents influence aromatic rings, replacing empirical values like Hammett constants with physically meaningful descriptors based on eff-AOs. These innovations aid in the design of better catalysts and functional molecules. In the second part, these new descriptors are used to predict the behavior of spin crossover (SCO) compounds, which change their magnetic state based on conditions like temperature. Furthermore, the EFOs provide insight into the efficiency of certain catalytic processes, such as carbon-hydrogen bond activation. The final section tackles the complex task of defining oxidation states based on first-principles quantum calculations. The thesis refines the effective oxidation state (EOS) method and applies it to challenging cases, such as the oxygen-evolving complex in Photosystem II. It also extends this analysis to solid-state materials and explores the connections between oxidation states and the statistical distribution of electrons across atoms. Altogether, this research establishes eff-AOs and EFOs as powerful, unifying tools that bridge chemical intuition with the rigorous insights of quantum mechanics, enabling advancements in catalysis, materials design, and bioinorganic chemistry